The present invention relates to an oil application roller that forms part of a fixing device used in electrostatic process copying machines, electrophotographic printers, and related machines.
In a fixing device employed in electrostatic process copying machines, electrophotographic printers, and related machines, sometimes the toner sticks to a thermal fixing roll when transferred toner is fixed onto a sheet of recording paper as a recording medium. To prevent the toner from contaminating the subsequent sheet of recording paper, an oil application roller is employed to apply an extremely small amount of silicone oil or other lubricant oil to the thermal fixing roll, thereby preventing toner from sticking to the thermal fixing roll and a sheet of recording paper from being wound around the thermal fixing roll so that it curls up. Oil application rollers having such functions have already been made available in many varieties. For example, FIG. 12 shows an oil application roller a that comprises a formed body of a cylindrical shape made of porous ceramics used as an oil retaining member b that stores lubricant oil to be applied, and an oil transfer layer c made of heat-resistant felt and an oil application amount control layer d made of polytetrafluoroethylene (PTFE) porous film that are wound around the surface of the cylindrical formed body and bonded together by using a mixture of an adhesive material and silicone oil.
FIG. 13 shows an oil application roller h that employs a cylindrical formed body of a metallic drilled hollow pipe e, in which a lubricant oil g is stored in an oil retaining tank f thereof and around which the oil transfer layer c and oil application amount control layer d are wound and bonded together. Furthermore, as an improved version of this oil application roller h, (1) an oil application roller is proposed, having a tubular member for allowing thermal expansion of an air layer interposed in the oil retaining tank to be released to the outside and a tube retaining member that retains a tubular member for increasing the amount of lubricant oil stored in the oil retaining tank (refer to Japanese Patent Application Laid-Open Publication HEI 10-20694). In addition, (2) another oil application roller is proposed that is provided with a film between the cylindrical formed body and the outside to allow thermal expansion of the air layer interposed in the cylindrical formed body made of the metallic drilled hollow pipe to be released to the outside as well as to increase the amount of lubricant oil to be stored (refer to Japanese Patent Application Laid-Open Publication HEI 10-10906).
With the oil application roller a shown in FIG. 12, however, the amount of lubricant oil that can be used is limited because of oil retaining characteristics of the porous ceramics, and the amount of unused lubricant oil accounts for, in some cases, as much as about 50% of the entire amount of lubricant oil retained. To extend the service life of the oil application roller a, therefore, it becomes necessary to increase its size. Also, while the oil application roller a is being used, an excessive amount of the lubricant oil is sometimes discharged as a result of the air contained in the oil retaining member b made of porous ceramics expanding with increased temperature. With the oil application roller h shown in FIG. 13, when an air layer i formed inside the oil retaining tank f expands, it could result in not only an excessive amount of lubricant oil g being discharged, but also the oil transfer layer c and the oil application amount control layer d being separated or destroyed.
In addition, according to the oil application rollers (1) and (2) disclosed in the respective publications, thermal expansion of the air layer can be released and the amount of lubricant oil stored can be increased. Since these oil application rollers are of a structure in which holes are drilled in metallic pipes, however, there are no layers that retain the lubricant oil. If the roller is placed in a vertical position during transportation or storage, therefore, there is a buildup of hydraulic pressure especially in a bottom portion of the roller, causing lubricant oil to leak, which could lead to an unexpected accident. Further, since lubricant oil is supplied through such holes, discharge of an uneven amount of oil tends to occur and, on top of that, it is difficult to control the amount of oil applied. This increases a possibility of toner sticking to the thermal fixing roll and the recording paper being wound around the roller thus curling up. In addition, the oil application roller according to (1) requires a complicated structure for storing a greater amount of lubricant oil, resulting in an increased manufacturing cost.
It is therefore an object of the present invention to provide an oil application roller that controls the amount of lubricant oil to be supplied to the fixing roller so as to ensure application of a uniform amount of lubricant oil, offers a high utilization efficiency of lubricant oil, develops no oil leak during transportation and storage, is built compact and simply structured, yet offering a long service life, and that prevents ill effects from oil leak or thermal expansion.
The present invention is based on the following facts discovered by the inventors through intense study. Namely, if the conventional cylindrical oil retaining member is hollowed out to make, for example, half of the entire volume is hollowed out, the utilization rate of lubricant oil can be improved from the conventional 50% to 75%. If the hollow cylindrical oil retaining member is of porous ceramics made of an inorganic material having micro-diameter voids and pores inside and its permeability resistance falls within a specific range or its porosity falls within a specific range, the hollow portion becomes decompressed and creates a balance with a capillary force after the lubricant oil has been charged. Accordingly, the possibility of oil leak occurring even during transportation or storage is eliminated and the amount of the lubricant oil supplied to the fixing roll can be controlled and a uniform amount of lubricant oil can be supplied during use despite its compact and simple structure. Furthermore, a pressure buffer mechanism may be provided to prevent ill effects that would otherwise be produced when oil or air expands by heat.
According to a first aspect of the present invention, provided is an oil application roller, in which an oil application layer is provided on an outer periphery of an oil retaining member that is made of a porous formed body of a hollow cylindrical shape and lubricant oil retained in the oil retaining member is supplied to a fixing roll. The porous formed body is made of an inorganic material having micro-diameter voids and pores inside, wherein at least a part of the micro-diameter voids communicates with a surface of the porous formed body and the pores, and at least a part of the pores communicates with the surface of the porous formed body through the micro-diameter voids, and offers a permeability resistance of 100 to 6,000 Paxc2x7s/m2. Given this configuration, the oil application roller can increase the utilization rate of lubricant oil to about 75% against 50% of the cylindrical oil retaining member. After the lubricant oil has been charged, the hollow portion is decompressed and creates a balance with a capillary force, which eliminates the possibility of oil leak occurring even during transportation or storage and the amount of the lubricant oil supplied to the fixing roll can be controlled and a uniform amount of lubricant oil can be supplied during use despite its compact and simple structure.
According to a second aspect of the present invention, provided is an oil application roller, in which an oil application layer is provided on an outer periphery of an oil retaining member that is made of a porous formed body of a hollow cylindrical shape and lubricant oil retained in the oil retaining member is supplied to a fixing roll. The porous formed body is made of an inorganic material having micro-diameter voids and pores inside, wherein at least a part of the micro-diameter voids communicates with a surface of the porous formed body and the pores, 40% or more of the entire volume of the micro-diameter voids are made up of small holes with diameters ranging from 30 to 200 xcexcm, and at least a part of the pores communicates with the surface of the porous formed body through the micro-diameter voids. Further, the average diameter of pores are greater than 200 and is equal to or less than 2,000 xcexcm, and the total volume of the pores accounts for 5 to 30% of the porous formed body. The lubricant oil is applied the fixing roll when a capillary force causes the lubricant oil retained in the pores to be supplied to a felt that forms an oil application layer through micro-diameter voids. It is therefore possible to adjust the amount of lubricant oil supplied to the oil application layer by adjusting the porosity. If porosity falls within the range, the amount of the lubricant oil supplied to the fixing roll can be controlled and, at the same time, a uniform amount of lubricant oil can be supplied to the fixing roll.
According to a third aspect of the present invention, provided is an oil application roller, in which an oil application layer is provided on an outer periphery of an oil retaining member that is made of a porous formed body of a hollow cylindrical shape and lubricant oil retained in the oil retaining member is supplied to a fixing roll. The porous formed body is made of an inorganic material having micro-diameter voids and pores inside, wherein at least a part of the micro-diameter voids communicates with a surface of the porous formed body and the pores, and at least a part of the pores communicate with the surface of the porous formed body through the micro-diameter voids. Further, a differential pressure (P1-P2) between a pressure (P1) of a gaseous phase portion of the hollow portion and the atmospheric pressure (P2) ranges between xe2x88x920.05 and xe2x88x922.0 kPa under a condition in which lubricant oil is retained in the hollow portion. When the oil retaining member is charged with the lubricant oil, the lubricant oil moves through micro-diameter voids in the oil retaining member and is retained inside the pores. At this time, a part of the air in the hollow portion is also drawn in to reduce the pressure inside the hollow portion. Because of a capillary force involved, the lubricant oil retained in the pores, on the other hand, tends to move through micro-diameter voids to a felt that forms the oil application layer. If the degree of pressure reduction falls within the above-mentioned range, it balances with the capillary force and, even during transportation or storage, there is no chance of an excessive amount of oil being transferred and hence there is no oil leak. The same balance between the pressure reduction in the hollow portion and the capillary force is maintained even during use, which makes it possible to stably supply a uniform amount of lubricant oil.
According to a preferred form of one aspect of the present invention, provided is an oil application roller, in which a pressure buffer mechanism that reduces fluctuations in pressure inside a hollow portion is provided between the hollow portion and the atmosphere. According to this configuration, when the lubricant oil is supplied from an oil retaining member through an oil application layer to a fixing roll, the lubricant oil charged in the hollow portion is supplied little by little to the oil retaining member until it is exhausted and, furthermore, the lubricant oil is supplied from the oil retaining member up to a supply limit. On the other hand, even when the pressure in an air layer formed as a result of the lubricant oil being supplied from the hollow portion and the oil retaining member and other components fluctuate depending on the operating conditions, the pressure buffer mechanism helps reduce the pressure fluctuations.
According to another form of an aspect of the present invention, provided is an oil application roller, in which at least one lubricant oil supply port that communicates with the hollow portion is provided in at least one of two flanges on both ends so that the lubricant oil can be supplied to the hollow portion. According to this configuration, in addition to the above-mentioned functions, it is possible to supply lubricant oil through the lubricant oil supply port when lubricant oil in the hollow portion runs out.
According to a still another preferred form of an aspect of the present invention, provided is an oil application roller, in which the oil application layer comprises an oil transfer layer and an oil application amount control layer placed thereon and these two layers are bonded together with a mixture of an adhesive material and silicone oil. According to this configuration, in addition to the above-mentioned functions, hardening of the adhesive material in a dispersed condition bonds the oil retaining member and the oil application layer together throughout the entire area in a dispersed condition. At the same time, the lubricant oil in a dispersed condition obtains a passageway of the lubricant oil through the oil application layer in a dispersed condition.
According to still another preferred form of an aspect of the present invention, provided is an oil application roller, in which the pressure buffer mechanism is a tube provided between the hollow portion and the atmosphere. With this configuration, the tube expands and shrinks in accordance with the pressure in the hollow portion and in other components to buffer these pressures, in addition to the functions.
According to yet another preferred form of one aspect of the present invention, provided is an oil application roller, in which the pressure buffer mechanism is a diaphragm placed between the hollow portion and the atmosphere. Such a configuration allows the diaphragm to expand and shrink in accordance with the pressure inside the hollow portion and in other components so as to buffer these pressures, in addition to the above-mentioned functions.
According to another preferred form of one aspect of the present invention, provided is an oil application roller, in which the pressure buffer mechanism contains a piston that is slidably installed in a cylinder, one end of which is open to the atmosphere while the other end of which is open to the hollow portion, and a spring is interposed between the piston and a clamping portion on either the atmosphere side or the hollow portion side of the cylinder. Such a configuration allows the piston in the cylinder to move in an attempt to counteract the force of the spring in accordance with the pressure inside the hollow portion and in other components so as to buffer these pressures, in addition to the above-mentioned functions.